The present invention relates to a bidirectional optical wavelength multiplexer and demultiplexer, and a bidirectional optical wavelength multiplexer and demultiplexer which multiplexes and demultiplexes light.
General optical wavelength multiplexer/demultiplexers using an arrayed waveguide grating (hereinafter, referred to as AWG) essentially apply the principle of Mach-Zehnder Interferometer, and multiplex and demultiplex light using the phase difference.
FIG. 1 is a structure view of a conventional optical wavelength multiplexer and demultiplexer. Referring to FIG. 1, a conventional optical wavelength multiplexer and demultiplexer includes N first arrayed waveguides 100 connected to an optical fiber for receiving light having different wavelengths, a first planar waveguide region (free space region, slab waveguide, or star coupler) 102 for distributing received light, an AWG 104 for allowing light from the first planar waveguide region 102 to have different phase differences, a second planar waveguide region 106 in which the light having different phase differences output from the AWG 104 interfere with each other and land at different locations on the opposite side according to wavelength, and M second arrayed waveguides 108 for outputting the light split according to wavelength.
This operation of the optical wavelength multiplexer/demultiplexer can be explained in a grating equation which describes the dispersion characteristics of an AWG which acts as a diffraction grating with respect to incident light.
In the grating equation, the phase changes caused in the first planar waveguide region 102, the AWG 104 and the second planar waveguide region 106 are all summed, and the sum of the phase changes satisfies the condition in which interference occurs at the interface between the second planar waveguide region 106 and the second arrayed waveguides 108. The grating equation is expressed with respect to light received via an input waveguide, as in Equation 1:
nsd sin xcex8+ncxcex94L=mxcexxe2x80x83xe2x80x83(1)
wherein ns denotes the effective refractive index of a planar waveguide region, nc denotes the effective refractive index of an AWG, d denotes the pitch of an AWG, m denotes the diffraction order, xcex94L denotes the length difference between adjacent AWGs, and xcex denotes the wavelength of the incident light.
A central operating frequency xcex0 is the wavelength when xcex8 is zero, and is defined as in Equation 2:
ncxcex94L=mxcex0 xe2x80x83xe2x80x83(2)
Equation 3, which describes a variation in angular dispersion, that is, a variation in the diffraction angle of light with respect to a change in wavelength, can be obtained from Equation 1:                                           ⅆ            θ                                ⅆ            λ                          =                  m                                    n              s                        ⁢            d                                              (        3        )            
That is, light beams having different wavelengths land at different angles on the second planar waveguide region of an optical wavelength multiplexer/demultiplexer, according to Equation 3. Thus, an output waveguide is connected at a location corresponding to the diffraction angle of light having a wavelength used in the second planar waveguide region, and thus performs optical wavelength demultiplexing with respect to the wavelength.
A general optical wavelength multiplexer/demultiplexer using the structure of an AWG has a structure in which the left side and the right side are symmetrical to each other, so that the same function is performed independently of the direction of connection of the device. Also, in the general optical wavelength multiplexer/demultiplexer having a symmetrical structure, input and output waveguides have no difference in structure, so that an arrayed waveguide can act as an input waveguide or an output waveguide according to the direction of connection.
This optical wavelength multiplexer/demultiplexer can only operate in one direction at one time, so that there is a method for allowing the optical wavelength multiplexer/demultiplexer to operate having different channel intervals according to the state of connection of the device by differentiating the intervals between first and second arrayed optical waveguides. However, this method is also the same as the conventional method in that an arrayed waveguide acts as an input or output waveguide according to the direction of connection of the device.
Also, when this optical wavelength multiplexer/demultiplexer is applied to a real system, it is commonly installed and used in only one direction. Therefore, the manufacture of an optical wavelength multiplexer/demultiplexer which can operate with the same operation characteristics in two directions cannot be a necessary condition for designing an optimized device that satisfies a given specification.
An objective of the present invention is to provide a bidirectional optical wavelength multiplexer/demultiplexer which can simultaneously multiplex and demultiplex light by connecting a central waveguide at the interface between each planar waveguide region and an arrayed optical waveguide.
To achieve the above objective, the present invention provides an optical wavelength multiplexer/demultiplexer including an optical waveguide array having a plurality of optical waveguides, a planar waveguide region connected to the optical waveguide array, and an arrayed waveguide grating connected to the planar waveguide region, wherein the optical waveguide array further includes a central waveguide formed at a location on or focal point which light transmitted from the arrayed waveguide grating to the planar waveguide region is focused, on the interface between the optical waveguide array and the planar waveguide region, and light multiplexed with a plurality of wavelengths is received or output via the central waveguide.